1. Field of the Invention
This invention relates to an equalizing mechanism in a home-positioning apparatus, and more particularly to a technique effective for application to an equalizing mechanism in a home-positioning apparatus, which is used in an X-Y home-positioning apparatus for a chip mounter, a dispenser or the like for example, wherein equalization of a driving force acting on a movable member driven on a pair of rails for moving can be performed.
2. Related Art Statement
In general, a home-positioning apparatus is of such an arrangement that a movable beam, which can move only in the Y-direction, is provided to have opposite end portions thereof supported by saddles which are movably engaged with rails for moving in the longitudinal direction (hereinafter referred to as a "Y-direction"), said rails being provided at opposite sides of a base of a machine, and that, in the movable beam, rails for moving in the lateral direction (hereinafter referred to as an "X-direction") are provided along the longitudinal direction of the movable beam and a carriage is racked between the rails to move only in the X-direction.
Then, an electronic parts mounting head of a chip mounter or the like is mounted on this carriage, and a so-called X-Y home-positioning robot system to perform the operation such as mounting is adopted, in which the movable beam and the carriage are moved and home-positioned in the X-direction and Y-direction respectively, by a numerical control means, and moved to determined positions thereof relative to a print circuit board and the like which are home-positioned by another means on the base of the machine.
This movable beam is normally driven by a servo-motor, which is numerically controlled through a ball screw and the like. However, in view of the characteristics an construction of the machine, it is impossible to drive the movable beam by giving force to the central portion or thereabout. Therefore, it is inevitable to provide the ball screw and the like to drive an end portion of the movable beam, and generally, such a system is adopted that one end portion or thereabout of the movable beam is driven by a ball screw to move and home-position the movable beam in the Y-direction.
However, in the above-described technique, since only one end portion of the movable beam is driven in the Y-direction, a turning force is generated in the horizontal plane by the acceleration at the time of moving and home-positioning, whereby the perpendicularity of the movable beam to the moving direction, i.e., the perpendicularity of the moving direction (X-direction) of the carriage racked on the movable beam to the moving direction (Y-direction) of the movable beam is impaired, whereby the reliability of home-positioning is reduced. Further, a high moment is applied to the saddles for supporting the movable beam, particularly the saddle on the driving side, so that an excessive load is applied to linear bearings and the like, which are normally used in this portion, to present a disadvantage of quickening deterioration, thereby presenting a large obstruction to making the mounting at higher speed, which is notable particularly recently.
To obviate the above-described disadvantages, such a measure has heretofore been adopted that a plurality of linear bearings having high capacity are provided at intervals in order to increase the anti-moment characteristics of the saddles (particularly one on the driving side). However, the costs are high, and moreover, the linear bearings and the like are provided apart from one another in the Y-direction, whereby it becomes difficult to increase the rate of the moving value of the movable beam to the total length of the rails for moving, and the dimensions of effective moving to the outer dimensions of the machine are restricted. Furthermore, because of the one side driving mechanism, it is difficult to eliminate such a disadvantage that the amplitude of vibrations at the time of home-positioning and the time of convergence are greatly increased at a portion close to the opposite side to the driving side, as compared with a portion close to the driving side.
In contract thereto, such a system is partially adopted that two sets of servo-motors and ball screws are used to drive opposite end portions of the movable beam. However, the costs are higher and such a disadvantage is presented that, in order to operate in synchronism the two servo-motors stably without being influenced by a transient phenomenon, unbalanced interference of an external force and the like, it is necessary to use a complicated and expensive control system.